One issue associated with using alternative energy sources is the ability to store currently produced energy for later use. Alternative energy sources, such as solar cells or wind farms, often provide energy at certain peak times during each day. For example, solar cells only produce energy during daylight hours, and wind conditions usually peak at certain times of the day or vary according to weather conditions. Demands for energy, on the other hand, may peak at other times. Thus, energy produced by alternative energy sources may not coincide with energy demand.
Technologies for storing energy are known to those skilled in the art. One approach is to convert electrical energy into various forms of mechanical or potential energy, and recover the energy by converting the mechanical back into electrical energy when needed. For example, one storage approach involves using electricity to pump water into a reservoir. At a later time, the water can be released through a turbine to generate electricity by turning a generator. A typical device to perform electrical to mechanical power conversion is a motor, and a typical device to perform mechanical to electrical power conversion is a generator. In some cases, a motor and a generator may be the same device functioning as a motor (in a “motor mode”) to turn a pump and later functioning as a generator (in a “generator mode”) when electrical energy is to be extracted. In another example, the motor/generator uses electricity in the motor mode to spin a flywheel at a high speed. When electricity is needed, the mechanical energy of the flywheel is tapped to turn the motor/generator in a generator mode to produce electricity.
These approaches are sometimes referred to as “time shifting” of energy production, since generating electrical energy occurs at a different time from when it is used. In various applications, the time shifting period may vary from a fraction of a second to several hours, or more. In the above example of pumping water to a reservoir during off-hours to store energy, the time shifting may be several hours, days, or even longer. In another example where energy is stored to compensate for power outages, an energy storage source may be immediately tapped for power upon request. For example, transient voltage variations, such as short duration (from milliseconds to seconds), long duration (from seconds to minutes), sustained voltage sags (>minutes), and interruptions can occur within the power grid. In any case, the effects can be ameliorated by rapidly accessing a temporary energy storage source. An energy storage facility may be storing energy from an electrical source one second, and then may be required to provide energy the next second. Thus, it is desirable that such systems provide a fairly quick response from storing energy to providing energy.
It is with respect to these and other considerations that the disclosure herein is presented.